1. Field of the Invention
The present invention relates to an automatic product conveying system in a factory.
2. Description of the Related Art
In general, a production control system is composed of a process controller which connects plural work stations with a warehouse through a conveyance means such as, for example, an unmanned automatic conveyance car and controls the work stations; a conveyance controller for controlling the conveyance means; and a host computer which performs the exchange of information between it and the said controllers and gives instructions to the controllers on the basis of a work plan and a process procedure. A production control system called FMS (Flexible Manufacturing System) has realized a production system capable of coping with multi-variety, small lot production wherein predetermined works are performed while various products are flowing through work stations in accordance with a predetermined procedure.
In such production control system, a carrier receives products at a certain work station and conveys the products to another work station along a conveyance path, in which station there is effected a desired work such as inspection for example. Between the carrier which travels by itself on the conveyance path and each work station there is provided a station conveyor for the reception and delivery of products between the carrier and each work station. According to the prior art, when loading and unloading of products are to be performed using one station conveyor, a control system for the carrier and a control system for the station conveyor are linked together and a distinction is made between the loading of products to the carrier and the unloading of products from the carrier.
Unless the carrier control system and the station conveyor control system are linked together, an empty loading may be done when product is to be loaded to the carrier, or another product is already present on the station conveyor side when product is to be unloaded from the carrier, which may cause collision of the products with each other on the station conveyor. However, linking the carrier control system and the station conveyor control system with each other gives rise to the problem that the control systems become complicated, resulting in an increase of cost.
Products are stored in a warehouse and taken out from the warehouse in accordance with a predetermined work plan, but since processing machines and testing apparatus which constitute each work station continue to operate in accordance with a predetermined sequence, so the product delivery timing in taking out product from the warehouse is controlled strictly. This is because once the product delivery timing is disordered, the product processing and testing operations are discontinued. In the conventional systems, therefore, a warehousing port for storing product into a warehouse from the carrier and a delivery port for taking out product from the warehouse and loading it onto the carrier are provided separately between a conveyance path along which the carrier travels by itself and the warehouse, and the operation of the warehousing port and that of the delivery port are controlled by a host computer.
Consequently, in the conventional systems the equipment cost is high and the host computer is required to have both a program for warehousing and a program for delivery.
For solving the above problem, one will easily hit upon the idea of using a port in common for both warehousing and delivery. However, if there is adopted a buffer as such a common port, there newly arises the following problem at the time of concurrence between a product to be warehoused and a product for delivery. Since the collision of the products is to be avoided, the unloading of the product for delivery onto the conveyance path is delayed eventually. Such a delay of the product for delivery impedes the working efficiency of the processing machines and testing apparatus waiting for the supply of product without letup.